Equipment for Stirring the Electrolyte in Electrolytic Production Cells

ABSTRACT

The current systems for stirring electrolyte in the cells for the electrolytic production of metals consists of introducing into the production cells, air or compressed neutral gases at low pressure in ventilators, and distribute them in the cell by means of perforated pipes to stir the electrolyte. These pipes are firmly attached to the structure of the cell or to a supporting structure of insulating material, in the case of the newly designed cells. With use, the crystallization of salts dissolved in the electrolyte, the depositing of solids and of anodic sludge will obstruct the perforations of the pipes, limiting the circulation of the electrolyte stirring air. During the operation of the cell, breakdowns or failures occur in the ventilators, distribution ducts and perforated pipes of this system for different reasons whose reparation or cleaning implies losing production time. 
     The generation of gases in situ by electrolysis, by the electric energization of one or more circuits of conductors placed underneath the anodes and cathodes, and mounted in the traditional cells or in an independent support structure, in which the anodes and cathodes are installed, permits the stirring of the electrolyte and the reduction of the negative effect of the boundary layer, in a simple manner and without the complications of the air injection systems. With this, the quality of the cathode deposit is also improved; and the distribution of the weight of the cathodes and the energy efficiency are improved. The production time lost during the cleaning and repairing of the air injection system is also reduced as these works are simpler to perform when the ventilators and perforated pipes are replaced by electrical conductors.

DESCRIPTION OF WHAT IS KNOWN IN THE FIELD

Normally the depositing of metals by electrolysis from a solution isexecuted in masonry cells, coated with insulating materials, resistantto acids or alkalis and to temperature, in which the electrolyte isnormally fed through one end of the cell, while the spent electrolyte isdischarged by the opposite lower end, if the feeding has been via theupper border, or vice versa.

Occasionally transversal circulation of the electrolyte has been used,that is, parallel to the faces of anodes and cathodes, by means of theintroduction of perforated piping, in which the feed is carried outthrough a longitudinal perforated pipe, located at the bottom on oneside of the cell, while the discharge is executed by overflow or throughanother perforated pipe located on the opposite upper side of the cell.

In both situations, the position of the pipes, once in place, remainsinalterable, as these become part of the structure of the cell.

To improve current efficiency, air is sometimes injected to stir theelectrolyte and obtain a uniform concentration, which helps avoiding thecrystallization of the electrolyte and diminishes the effect of theboundary layer. This is executed introducing perforated pipes throughwhich air or neutral gases are injected, which requires the supplying ofventilators, air supply ducts and the perforated distribution pipes. Thefact of having pipes filled with air submerged in the electrolyte causesthem to have a tendency to float; therefore the systems with which thepipes are attached to the cells is complex.

During the normal operation, the crystallization of salts dissolved inthe electrolyte, the falling of lead due to the wear of the anodes thatcontain it, as well as other solids, causes sediment to accumulate inthe bottom of the cell, and it also settles on the perforated airdistribution pipes, obstructing the flow. This makes stopping theoperation necessary in order to clean the pipes, which implies losingproduction time.

Other motives for executing maintenance of the air distributorsoriginate in the physical breaking of the pipes, either due to materialfailure or knocks.

Recently, to improve efficiency and, among other things, avoidproduction losses due to the maintenance of the cells, removableinsulating structures are used, such as that indicated in Chilean patentapplication N° 1020-04, in which the anodes, cathodes, electrolytecirculation piping and air distribution pipes are mounted, all of whichcan be removed from the cell at the end of the production cycle formaintenance purposes, thus drastically reducing production losses due tothis cause.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the supporting structure ofinsulating material, which can be introduced and withdrawn from thecell, in which the vertical and horizontal guides can be seen on whichthe anodes and cathodes are mounted, to which the circuits of piping forelectrolyte distribution and the electrical conductors for thegeneration of the electrolyte stirring gases can be attached.

FIG. 2 shows a perspective view of the support structure of insulatingmaterial, in which an assembly of electrical conductors mounted on thestructure can be seen.

FIG. 3 shows a perspective view of the electrical conductors, mounted onthe lower crosspieces of the support structure of insulating material.

FIG. 4 shows a perspective view of the electricity supply conductor,connected to three electric conductor circuits, producers of bubblinggas.

FIG. 4A shows a perspective view of the electricity supply conductor,connected to three electric conductor circuits, producers of bubblinggas, in which the supports for their mounting and attaching to thesupporting structure of insulating material are shown.

FIG. 4B shows a perspective view of the electricity supply conductor,connected to three electric conductor circuits, producers of bubblinggas, in which the insulated and uninsulated sectors of those conductorsare shown.

FIG. 5 shows a perspective view of the electricity supply conductorconnected to two electric conductor circuits, producers of bubbling gas.

FIG. 6 shows a perspective view of the electricity supply conductorconnected to a circuit of electrical conductors, producer of bubblinggas.

FIG. 7 shows a perspective view of the electricity feed conductor forthe circuits of the electrical conductors, producers of bubbling gas.

The numbers indicated in the figures have the following meaning:

-   1. Connection for the feeding of fresh electrolyte.-   2. Upper end of the vertical guide of anodes and cathodes.-   3. Cradle for connection to the crane with which the electrolytic    cell is installed or removed from the supporting structure of    insulating material.-   4. Inferior guide to fix the position of the bottom of the anode.-   5. Inferior guide to fix the position of the bottom of the cathode.-   6. Upper frame of the support structure of insulating material.-   7. Lower frame of the support structure of insulating material.-   8. Insulated conductor for feeding electricity to the circuits that    produce gases by electrolysis.-   9. Anterior circuit of electrical uninsulated conductors for the    production of bubbling gas.-   10. Intermediate circuit of electrical uninsulated conductors for    the production of bubbling gas.-   11. Rear circuit of electrical uninsulated conductors for the    production of bubbling gas.-   12. Electrical connector for feeding the anterior circuit of    electrical uninsulated conductors, for the production of bubbling    gas.-   13. Electrical connector for feeding the intermediate circuit of    electrical uninsulated conductors, for the production of bubbling    gas.-   14. Electrical connector for feeding the rear circuit of electrical    uninsulated conductors, for the production of bubbling gas.-   15. Bracket to the frame of the supporting structure of insulating    material.-   16. Insulated section of the electrical conductor that produces    bubbling gas.-   17. Uninsulated section of the electrical conductor that produces    bubbling gas.

DESCRIPTION OF THE INVENTION

This invention consists of fixing one or more circuits that supplyelectricity to one or more circuits of electrical uninsulatedconductors, or with localized sections of insulation, which are locatedin the inferior zone of the electrolytic production cell, or to asupport structure of anodes and cathodes of insulating material,independent of the production cell, which can be removed and installedin it, with or without the anodes and cathodes already placed in theguides of the support structure.

In one of its embodiments, and without this meaning the limiting of thegenerality of the invention, a circuit of insulated electricitysupplying conductors (8) has been attached on the outside and on oneside of a support structure of anodes and cathodes, built ofelectrically insulating material, inside which a plurality of anodes andcathodes are placed, while underneath the inferior frame (7) of thesupport structure, one or more circuits of electrical uninsulatedconductors or with localized sections of insulation (16) have beenattached, that link the electricity supplier (8), by means of connectors(12, 13 and 14) to the circuits of uninsulated conductors or withlocalized sections of insulation (9, 10 and 11).

In another of its embodiments, in a traditional cell for theelectrolytic production of metals, the insulated conductor(s) thatsupply electricity are fixed to the vertical walls of the cell, whilethe electrical circuit(s), uninsulated or with localized sections ofinsulation, are fixed directly to the floor of the cell.

The circuit(s) of electrical uninsulated conductors or with localizedsections of insulation can be built of either single thread solid wireor multiple thread wire, of metal covered with a mixture of metal oxides(known in the English language as MMO, short for “Mixed Metal Oxide”).

The application of electrical pressure between cathodes and the circuitsof uninsulated conductors or with localized sections of insulation (9,10 and 11), in such a way that these circuits remain at a positivepressure with regard to the cathodes, causing an electrolysis of thewater of the electrolyte, generating oxygen in the periphery of theconductors that are uninsulated or have sections of insulation. Theoxygen becomes detached in the form of very small bubbles, which ascendbetween anodes and cathodes or only underneath the cathodes ifconductors are employed that have localized sections of insulationunderneath the anodes, producing a more global or more localizedstirring of the electrolyte, respectively.

The number of bubbles can be controlled by modifying the voltage or thecurrent applied between cathodes and the circuits (9, 10 and 11) ofconductors that are not insulated or that have localized sections ofinsulation (16).

It becomes evident that the cleaning of the insulated feed conductors aswell as that of the uninsulated conductors or those with localizedsections of insulation (16), if it should be necessary, can be executedvery simply, at the end of the production cycle, decreasing losses inproduction time in this respect.

EXAMPLE OF APPLICATION

As an example, and without this limiting the generality of theinvention, in a traditional cell for electrodepositing copper, measuringsix and a half meters in length by 1.2 meters wide and 1.5 meters deep,a support structure of insulating material will be introduced built ofplastic reinforced with fiberglass, with guides for anodes and cathodesof insulating material, loaded with 61 insoluble anodes measuring 1200millimeters high by 800 millimeters wide, with support flaps to theconductor bar and 60 stainless steel cathodes measuring 1140 millimetershigh and 880 millimeters wide, spaced at 95 millimeters between centers.

Once the supporting structure of insulating material of the cell isintroduced, with the anodes and cathodes mounted; with the insulatedconductor for feeding electricity (8) and the circuits of uninsulatedconductors or with conductors with localized sections of insulation (9,10 and 11), fixed to the bottom frame of the supporting structure bymeans of the respective supports (15), the pipe for the circulation ofelectrolyte is connected to the connection (1) and the electric power isconnected to start production operation.

The uninsulated electrical conductors or the conductor with localizedsections of insulation, are made of titanium coated with a mixture ofmetal oxides 3 mm in diameter.

The electrolyte is circulated at a flow between 10 and 30 cubic metersper hour and the electric power is supplied at a potential of 1.7 to 2volts between the circuits of uninsulated conductors or with conductorswith localized sections of insulation (9, 10 and 11) with regard to thepotential of the cathodes. This difference of potential produces theliberation of oxygen on the surface of the uninsulated conductors or inthe conductors of localized insulation (16).

The ascension of the gas from below the anodes and cathodes, or onlyfrom below the cathodes for the conductors with sections of insulationlocated underneath the anodes, stirs the electrolyte, improving theuniformity of its concentration, reducing the boundary layer and thusimproving current quality and efficiency of the metal deposition.

When the deposit on each side of the cathode reaches about threemillimeters, the operation will be detained, the cathodes removed, cleancathodes loaded and the operation will be restarted.

These cycles will be repeated until the bottom of the cell has to bestripped, on which occasion the complete support structure of anodes andcathodes will be removed and replaced by another equivalent one,prepared beforehand, restarting a new cycle of production.

With this procedure, the ventilators and the feed and distributioncircuits of stirring air are replaced only by the electrical conductorsas the electric power to energize the circuits of uninsulated conductorsor conductors with localized sections of insulation can be obtained fromthe same source that is used for the production of metal.

Maintenance time is reduced, in relation to the maintenance of theventilators and pipes for supplying and distributing air. At the sametime, the chemical and physical quality of the cathodes is improved,their dimensional uniformity and therefore, their weight dispersion arereduced and the energy efficiency improves.

1. Equipment for stirring electrolyte in cells for the electrolyticproduction of traditional metals, or that use removable supportingstructures of anodes and cathodes, CHARACTERIZED in that they have oneor more insulated conductors for supplying electricity, fixed to oneside of the cell or of a removable supporting structure of anodes andcathodes, and connected to one or more circuits of uninsulatedelectrical conductors or with localized sections of insulation, locatedunderneath the anodes and cathodes of the cell and fixed to theremovable supporting structure of anodes and cathodes, or to the bottomof the traditional cell for electrolytic production of metals. 2.Equipment for stirring electrolyte in cells for the electrolyticproduction of traditional metals, or that use removable supportingstructure of anodes and cathodes, according to claim 1, CHARACTERIZED inthat uninsulated electrical conductors or with localized sections ofinsulation are manufactured of titanium or another similar metal,covered with mixed metal oxides.